1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrophotographic copying machine, a laser printer with a scanner, a facsimile machine, etc., and especially to an image forming apparatus capable of forming sharp images without toner scattering around edge portions of solid images or line images.
2. Discussion of the Background
In a color image forming apparatus, a plurality of color toners are laid one over another, and thereby a desired color image is obtained. However, as the color toners are laid one over another repeatedly, adhesion of the toners decreases as the toner colors are laid over one another, and thereby scattering of toner occurs around line image portions and an image tends to blur.
Conventionally, to prevent toner from scattering around line image edge portions, the toner amount of each color around the line image potions is uniformly controlled so as to decrease. Alternatively, an amount of black toner which is laid over increases more than that of the other toners, whereby it is possible to decrease the degree of toner scattering and changes of hue around edge potions of images. This type of operation is disclosed in, as an example, Japanese Laid Open Patent Number 5-207276.
As mentioned above, in the conventional apparatus, toner scattering can be decreased. However, in the operation in the conventional apparatus a toner image is formed more thickly than that of the original image, or a hue of edge portions of the image is blacker than that of the original image. Further, depending on the image forming apparatuses used, effects of the compensation are dispersed because the degree of correction is the same. Even in the same apparatus, a degree of the effects changes because of changes over time. Accordingly, it is difficult to provide a color image forming apparatus capable of forming distinct images with high quality without toner scattering.